Method for the production of an electrode for cathodic protection

ABSTRACT

Method of anodizing lead base wherein lead dioxide pieces are incorporated into the surface of the base prior to anodizing. The lead dioxide pieces can be obtained by electrodeposition from a lead nitrate - copper nitrate bath.

United States Patent Udupa et al.

[451 Sept. 30, 1975 METHOD FOR THE PRODUCTION OF AN ELECTRODE FOR CATHODIC PROTECTION Inventors: l-landady Venkatakrishna Udupa;

Kapisthalam Chetlur Narasimham, both of Tamil Nadu, lndia Assignee: Councilof Scientific & Industrial Research, New Delhi-L, lndia Filed: May 23, 1974 Appl. No.: 472,813

US. Cl 204/29; 204/57; 204/290 R;

204/196 Int. Cl. C25d 5/34; C25d 11/02 Field of Search 204/29, 57, 290 R Primary Examiner-T. Tung Attorney, Agent, or F irm-l-lammond & Littell [5 7] ABSTRACT Method of anodizing lead base wherein lead dioxide pieces are incorporated into the surface of the base prior to anodizing. The lead dioxide pieces can be obtained by electrodeposition from a lead nitrate copper nitrate bath.

5 Claims, No Drawings METHOD FOR THE PRODUCTION OF AN Y ELECTRODE FOR CATHODIC PROTECTION SYNOPSIS OF THE INVENTION This invention relates to improvements in or relating to a method of forming lead dioxide on lead or its alloys in chloride medium. I I i It is known to employ lead dioxide coated lead oralloys as anode in the cathodic protection. r

The anodes used in the cathodic protection are electrodes of lead or its alloys having a coating of lead-dioxide on same. r I

PRIOR ART In the known art, lead dioxide coating is formedon lead or its alloys using a costly material like platinum as the micro-electrode. As is well known, the prior art employs platinum as microelectrode which is embedded in the lead or lead alloys and the same is anodized in sodium chloride (3%) solution or synthetic sea water to get a coating of lead dioxide on lead or lead alloys.

BACKGROUND AND OBJECTS DETAILED DESCRIPTION OF THE INVENTION According to this invention the method for preparing an electrode for cathodic protection comprises incorporating a microelectrode of lead dioxide into the surface of lead or lead alloys, followed by anodizing the obtained combination in a chloride medium at a current density not exceeding 6 amperes/dm at temperatures not exceeding 50C for sufficient length of time to obtain an electrode having an adherent coating of lead dioxide on lead or its alloys.

The micro-electrode of lead dioxide can be prepared in various ways.

For example, according to one method the lead dioxide microelectrode is prepared from solid pieces of lead dioxide deposited from lead nitrate-copper nitrate bath on a suitable substrate like graphite, stainless steel or nickel (as described in Indian Pat. No. 66195, 124215) and were ground on the emery belt of 60 and 100 to the desired size and shape.

Alternatively the microelectrode is prepared by exposing the desired area on the substrate and stopping off the rest of the portion during electro-deposition of lead dioxide from nitrate bath.

PREPARATION OF MICRO ELECTRODE and were ground on the emery belt of 60 and to the desired size and shape.

Alternatively the microelectrode is prepared by exposing the' desired area on the substrate and stopping off the rest of the portion during electro-deposition of lead dioxide from nitrate bath.

PREPARATION OF FINAL ELECTRODE The microelectrodes of lead dioxide so prepared are then embedded into the lead or lead alloy surface. This can easily be done by drilling suitable holes in the lead or lead alloy surface and press-fitting the lead dioxide microelectrodes.

The combination thus obtained is anodized in a 0.5 to 3.0 sodium chloride solution or synthetic sea water and the current density employed can vary between 0.5 and 6.0 A/dm The temperature of polarization can be adjusted between 15 and 50C.

By adjusting the time of polarization, satisfactory deposits of lead dioxide can be obtained. It is generally advantageous to maintain the ratio of the area of lead or lead alloy surface to the totalsurface of the lead dioxide microelectrode" to be between 10 and 600. In pure chloride solution the deposit of lead dioxide was sometimes patchy but covering most of the portion of basis lead or its alloy.

To improve the adherence of the lead dioxide to the EXAMPLES The following typical examples are given-to illustrate the invention and are not to be construed as a limitation thereof.

Example 1 Electrolyte 3%( W/ V )sodium chloride solution Anode Lead Area of anode (cm Area of lead dioxide microelectrode (cm Cathode Area of cathode (cm Inter electrode distance (cm) Cell voltage (volts) Anode current density(A/dm Temperature (C) Duration of polarization (hrs) Example 2 Electrolyte Anode Area of anode (cm Area of lead dioxide micro. electrode (cm Cathode Area of cathode (cm Inter electrode distance (cm) Cell voltage (volts) Anode current density (A/dm Temperature (C) Duration of polarization(hrs) Example 3 Electrolyte Anode Area of anode (cm Area of lead dioxide microelectrode (cm) Mild Steel 20 3% (W/V) sodium chloride solution Lead Mild steel 3% (W/V) sodium chloride solution Lead -Continued Example 1 Cathode Mlld Steel Area of cathode (cm'-) 20 lnter electrode distance (cm) 6 Cell voltage (volts) 3.6-3.9

Anode current density(A/dm 3 Temperature (C) l5 Duration of polarization (hrs) 4 Example 4 Anode Lead Area of Anode (cm l9.54

Area of microelectrode (cm) 0.26

Anode current density (A/dm) 2.3

Cathode Mild Steel Area of cathode (cm) 60 lnter electrode distance (cm) Cell voltage (volts) 4.2-7.0 15

Temperature (C) 3032 Weight loss in 3% NaCl after 512 hours (mg/cm )/A hr.) 0.330

Weight loss in synthetic sea water after 483 hours (mg/cm )/A hr.) 0.072

Example 5 Anode Lead-antimony (6%) Area of anode (cm l9.54

Area of'microelectrode (cm') 0.26

Anode current density (A/dm) 2.3

Cathode Mild Steel Area of cathode (cm*) 60 lnter electrode distance (cm) 15 Cell voltage (volts) 4.26.0

Temperature (C) -32 Weight loss in 3% NaCl after 445 hrs. (mg/cm) /A.hr) 0.035

Weight gain in synthetic sea water after 482 hrs.(mg/cm )/A.hr) 0.071

Example 6 Anode Lead-silver 1%) 30 Area of anode (cm 20.33

Area ofmicroelectrode (cm 0.252

Anode current density (Aldm 2.5

Cathode Mild Steel Area of cathode (cm*) 60 lnter electrode distance (cm) 15 Cell voltage (volts) 4 l-4.5

Temperature (C) 30.35 Weight loss in 3% NaCl after 524 hours (mg/cm /Ahr) 180 Weight gain in synthetic sea water after 482 hours (mg/cm Ahr) 0.066

Having described the invention and ascertained the manner in which the same is to be carried out, what is claimed is the following:

1. A method for the preparation of a lead dioxide coated lead electrode for cathodic protection comprising electrodepositing lead dioxide on a conductive substrate from a lead nitrate-copper nitrate bath, incorporating solid pieces of said lead dioxide into the surface of a lead or lead alloy base and anodizing the obtained base in a chloride medium at a current density not exceeding 6 amperes/dm at temperatures not exceeding 50C for a sufficient length of time to obtain lead based electrode having an adherent coating of lead dioxide thereon.

2. A method as claimed in claim 1 wherein the conductive substrate is selected from the group consisting of graphite, steel and nickel.

3. A method as claimed in claim 1 wherein the lead dioxide pieces are embedded into the surface of lead or its alloy by simple press fitting of the pieces into suitably drilled holes in the surface of lead or its alloy.

4. A method as claimed in claim 1 wherein the anodization is carried out in a 0.5 to 3.0% sodium chloride solution optionally containing sulfate ions with a sulfate to chloride ratio of 1:7.

5. A method as claimed in claim 1 wherein the anodization is carried out at a current density of 0.5 to 6.0

A/dm at temperatures between 15 and 50C. 

1. A METHOD FOR THE PREPARATION OF A LEAD DIOXIDE COATED LEAD ELECTRODE FOR CATHODIC PROTECTION COMPRISING ELECTRODEPOSITING LEAD DIOXIDE ON A CONDUCTIVE SUBSTRATE FROM A LEAD NITRATE-COPPER NITRATE BATH, INCORPORATING SOLID PIECES OF SAID LEAD DIOXIDE INTO THE SURFACE OF A LEAD OR LEAD ALLOY BASE AND ANODIZINGTHE OBTAINED BASE IN A CHLORIDE MEDIUM AT A CURRENT DENSITY NOT EXCEEDING 6 AMPERES/DM2 AT TEMPERATURES NOT EXCEEDING 50*C FOR A SUFFICIENT LENGTH OF TIME TO OBTAIN LEAD BASED ELECTRODE HAVING AN ADHERENT COATING OR LEAD DIOXIDE THEREON.
 2. A method as claimed in claim 1 wherein the conductive substrate is selected from the group consisting of graphite, steel and nickel.
 3. A method as claimed in claim 1 wherein the lead dioxide pieces are embedded into the surface of lead or its alloy by simple press fitting of the pieces into suitably drilled holes in the surface of lead or its alloy.
 4. A method as claimed in claim 1 wherein the anodization is carried out in a 0.5 to 3.0% sodium chloride solution optionally containing sulfate ions with a sulfate to chloride ratio of 1:7.
 5. A method as claimed in claim 1 wherein the anodization is carried out at a current density of 0.5 to 6.0 A/dm2. at temperatures between 15* and 50*C. 